The invention pertains to generating and adjusting temperature values in a fixing roller of a fixing unit, which is mounted in a copy machine, can be switched over to various operational states, and can be used for fixing of toner images transferred on imaging materials.
There are some known fixing units which are used in copy machines, whereby the rotating fixing roller along with a pressing roller that can be mounted to its outer surface parallel with the axis form an opening, through which the imaging materials that carry the toner image could pass. The fixing roller can be heated by a heating agent connected to a control/adjustment unit whose heating level can be set up at different levels for generating and adjusting predetermined temperature values. The temperature values at the outer surface of the fixing roller can be registered by at least one temperature sensor; and the outer surface of the fixing roller can be cooled out by an airflow blowing unit fed from a controllable cooling unit.
A U.S. Pat. No. 5,787,321 patent discloses a device for generating and adjusting an operational or fixer temperature value at the outer circumference of heated and revolving fixing rollers of a fixing unit. The fixing rollers are arranged as a pair of rollers parallel with the axis and this pair consists of a heating roller and a pressing roller. A number of temperature sensors along with airflow blowing units assigned to them are arranged axially along both fixing rollers and are positioned axially at a distance from one another and in front of the fixing rollers in the direction of the flow, whereby the axial cross-section width of an airflow blowing unit, or to be more precisexe2x80x94its aired area, corresponds to the smallest width of the sheet carrying the toner image. In order to prevent an overheating of the top surfaces of the uncovered fixing rollers, which are not protected by the sheet running through the fixing opening, airflow blowing units are turned on and pointed towards it or them by a control unit, whereby the airflow blowing units are arranged in the so called sheet-free area of the fixing rollers. The generation and adjustment of temperature values, and especially the temperature of the fixer, as well as the switching over to the different operational states is done essentially by a heating level control/adjustment unit.
A disadvantage of the disclosed form of implementation is that a focused, homogeneous, and intensive cooling over the whole axial length of the fixing rollers by using the described airflow blowing units with a large opening for the flow can not be adequately achieved. Furthermore, due to the arrangement of the temperature sensors in the airflow, it is difficult to achieve an exact measurement of the temperature values at the outer surface of the fixing rollers. Also, due to its sluggishness, the used method of control/adjustment of the heating level is disadvantageous from the point of view of achieving fast generation, adjustment, and change of the temperature values, and particularly of the fixer temperature, as well as faster switching over to different operational states.
A DE-25 07 559-A patent discloses a device and a method For generating an operational or fixer temperature value at the outer circumference of heated and revolving fixing rollers of a fixing unit, whereby a heating roller and a pressing roller together form a pair of fixing rollers. A sucking unit for cooling the surfaces of both rollers is mounted at the top of the pressing roller. The sucking unit exhibits an airflow directing channels, which is aligned with the conveyor belt for transportation of the sheet and respectively axially aligned with the pressing roller. On the one hand, the airflow directing channel is connected through a single switching valve with a low-pressure generating unit, and, on the other hand, it has on both sides of the air channel a number of narrow air channels/air-pipes, which are parallel to each other, extend themselves axially up to both ends of the pressure roller, and lead into the air channel. The air pipes, which are positioned radially with respect to the surface of the pressing roller and at a distance from one another, are arranged in the direction of the pressing roller and along the outer circumference one behind the other at an angular interval of about 5-10 degrees. Each one of the air pipes has in its pipe wall a number of air nozzles, which are arranged one next to the other along the axial extension of the pipes and are lined up in such a way on the pressing roller thatxe2x80x94in order to prevent overheating only the end areas, respectively the ends of the roller pairs that jut over the sheet width, are cooled. The generation and adjustment of the temperature values, and particularly the fixer temperature, as well as the switching over to the different operational states are performed essentially by a heating level control/adjustment unit.
A disadvantage of the disclosed form of implementation is that due to the use of the described sucking unit, which is mounted in the area of the pressing roller and whose cooling action is limited essentially to the axial end areas of the rollers, a focused, homogeneous, and intensive cooling over the whole axial length of the fixing rollers is not possible. Further disadvantage is that the air pipes cannot be separately controlled in order to vary the cooling action. Furthermore, due to its sluggishness, the used method of control/adjustment of the heating level is disadvantageous from the point of view of achieving fast generation, adjustment, and change of the temperature values, and particularly of the fixer temperature, as well as faster switching over to different operational states.
Therefore, a fundamental objective of the present invention is to provide a method and a device that does not have the above mentioned disadvantages and, what is more, guarantees the faster, more precise and simpler functioning of the fixing unit, and particularly a faster and more precise generation and adjustment of predetermined temperature values at the fixing roller in various operational states in order to accelerate and improve the fixing process in automated environment.
In the presented invention, this task is solved in such a way that the generation and adjustment of predetermined values at the outer surface of the fixing rollers is achieved by a controllable and adjustable airflow of the cooling unit; and also the generation and adjustment of the airflow is effected on the basis of a determined core temperature of the fixing roller.
Furthermore, this method can be advantageously characterized by the fact that an initial predetermined temperature value of the fixing roller can be generated and adjusted by a heating unit brought to a constant maximum heating level, and after the initial predetermined temperature value has been reached, a first and a second operational level of the fixing unit can be reached through the airflow of the cooling unit driven by small to middle (0 to 50%) airflow levels; that a second predetermined lower temperature value of the fixing roller at constant maximum heating level can be generated and adjusted in a third operational state of the fixing unit achieved by an airflow through maximal (100%) to middle (50%) airflow levels; and that between the start of the second operational state xe2x80x9cRequest for a fixing taskxe2x80x9d, proceeding from the first operational state xe2x80x9cWaitxe2x80x9d, and a transition to the third operational state xe2x80x9cFixingxe2x80x9d there is a time interval whose length depends on the operational mode of the fixing unit before the request for a fixing task, and particularly on the core temperature of the fixing roller and the type of the imaging material that carries the toner image.
According to the invention, this task is solved by a cooling unit that has a blowing air unit in the form of a pipe connected to a source of compressed air. The pipe is mounted axially parallel to the fixing roller and is radially positioned in a fixed manner and at a distance from its outer surface, permitting it to generate a cooling strip at the outer surface of the fixing roller by a focused and concentrated compressed airflow whose air level can be controlled and adjusted through a control/adjustment unit acting upon the source of compressed air.
In advantageous way, based on the supported direction of the imaging medium carrying the toner image, the blowing part of the cooling unit is mounted in the direction of the airflow towards the fixing opening and at a distance from this opening in an area of the fixing roller. The blowing unit shows in its pipe wall at least one air nozzle in the form of a slot, which expands along its axial extent, or a number of air nozzles which are arranged along its axial extent, with the purpose of generation of concentrated and focused compressed airflow, which permits to create a cooling strip that extends itself over the whole axial length of the outer surface of the fixing roller. The obtained width of the whole cooling strip, which is formed by the separate cooling strips of the compressed air blowing unit, is essentially equal or less than one-fourth of the outer surface of the fixing roller.